From what I understand, once AT&T exhausts its on-hand stock of the A1428, it will start selling the "new" A1428 that T-Mobile will be selling as well. In other words, Apple will only be producing the "new" A1428 from now on. The new A1428 will be fully compatible with all of AT&T and T-Mobile's GSM, WCDMA and LTE bands.

The A1428 iPhone 5 variant has always possessed the physical capability for W-CDMA 2100+1700 (i.e. AWS). However, Apple implemented a software lock out to appease AT&T. The software lock out is being...(continues)